Name the photoreceptors in the retina, responsible for colour vision. (1)
cones
Name the structure that controls the size of the pupil. (1)
iris
Name the phenomenon of adjusting the curvature of the lens of the eye for near or distant vision. (1)
Accommodation
Which structures support the lens? (1)
Suspensory ligaments
Name two structures in the eye that play a role in refracting light. (2)
Cornea and lens
Name the middle layer that surrounds the eyeball and has a dark pigment. (1)
choroid
Give one reason why the above-mentioned structure is dark in colour. (2)
It absorbs light rays.
OR
It contains melanin
Explain why the iris is coloured. (2)
The coloured portion prevents light from passing through the iris. Hence light passes through the pupil only.
Question 4
The graph alongside shows the relationship between the clarity of image of the retina in the human eye. Study the graph then answer the questions that follow.
Name the area found on the retina that is indicated by the letter B on the graph. Explain your answer. (3)
Blind spot.
It lacks rods and cones and hence no image is formed.
Name the area of the retina which is represented by C on the graph. Explain the exact location of C in the eye. (2)
Fovea/yellow spot.
It is found on the retina, in line with the pupil.
Which structure A, B, C or D has the highest number of cones present? (1)
C
State the function of the retina. (2)
It is a photoreceptor, having light sensitive cells (rods and cones), which convert light rays to nerve impulses.
Question 5
Jabu participated in an investigation to determine the eye’s response to light. A lamp was placed at seven positions from Jabu’s face. The diameter of Jabu’s pupil was measured at each position of the lamp.
The results are shown in the table below.
At which position was the lamp furthest from the eye? Explain your answer. (3)
7. Diameter of the pupil is the largest - indicating dim light condition to allow more light to enter.
When the lamp was moved from position 1 to position 2, describe the mechanism that caused the change in the diameter of the pupil. (4))
Since less light enters the eye, the radial muscles of the iris contract, the circular muscles of the iris relax, causing the pupil to dilate / become wider / become bigger, thus allowing more light to enter.
Question 6
In an investigation a learner was asked to thread cotton through the eye of a needle 10 times with both eyes open and then with only the right eye open. This was done under the same light intensity at a distance of 50 cm from the eyes.
The results are shown in the table below.
Apart from the factors mentioned, state two other factors that had to be kept constant during the investigation. (2)
Size of the needle / needle used. Thickness of the thread (type of thread). Colour of thread. Size of the eye of the needle. Time period between attempts. Starting distance between needle and thread. (Any 2)
State a general conclusion that can be drawn for the results above. (2)
It takes more time to thread a needle with one eye open compared to having both eyes open. OR
It takes less time to thread a needle with both eyes open compared to having one eye open. OR
The more attempts undertaken to thread the needle the less time it takes.
Give a reason why more than one attempt was made in this investigation. (1)
To improve the reliability of the results.
Describe the changes that would take place in the eye if the distance between the needle and the eye were reduced from 50 cm to 20 cm. (4)
The ciliary muscles contract. Suspensory ligament becomes slack/relaxed. The lens bulges and becomes more convex /tension on the lens is released. The sclera pulls forward. The refractive power of the lens increases. A clear image is formed on the retina.
